For one, if we categorize events, we can raise our level of awareness of the context of the data that we're analyzing. Having categories for various artifacts can help us increase our relative level of confidence in the data that we're analyzing, because instead of looking at just one artifact, we're going to be looking at various similar, related artifacts together.
Another benefit of artifact categories is that they help us remember what various artifacts relate to...for example, I developed an event mapping file for Windows Event Log records, so as a tool parses through the information available, it can assign a category to various event records. This way, you no longer have to search Google or look up on a separate sheet of paper what that event refers to...you have "Login" or "Failed Login Attempt" right there next to the event description. This is particularly useful, as of Vista, Microsoft began employing a new Windows Event Log model, which means that there are a LOT more Event Logs than just the three main ones we're used to seeing. Sometimes, you'll see one event in the System or Security Event Log that will have corresponding events in other event logs, or there will be one event all by itself...knowing what these events refer to, and having a category listed for each, is extremely valuable, and I've found it to really help me a great deal with my analysis.
One way to make use of event categories is to employ an analysis matrix. What is an "analysis matrix"? Well, what happens many times is that analysts will get some general (re: "vague") analysis goals, and perhaps not really know where to start. By categorizing the various artifacts on a Windows system, we can create an analysis matrix that provides us with a means for at least begin our analysis.
An analysis matrix might appear as follows:
|Malware Detection||Data Exfil||Illicit Images||IP Theft|
Again, this is simply a notional matrix, and is meant solely as an example. However, it's also a valid matrix, and something that I've used. Consider "data exfiltration"...the various categories we use to describe a "data exfiltration" case may often depend upon what you learn from a "customer" or other source. For example, I did not put an "X" in the row for "Network Access", as I have had cases where access to USB devices was specified by the customer...they felt confident that with how their infrastructure was designed that this was not an option that they wanted me to pursue. However, you may want to add this one...I have also conducted examinations in which part of what I was asked to determine was network access, such as a user taking their work laptop home and connecting to other wireless networks.
The analysis matrix is not intended to be the "be-all-end-all" of analysis, nor is it intended to be written in stone. Rather, it's intended to be something of a living document, something that provides analysts with a means for identifying what they (intend to) do, as well as serve as a foundation on which further analysis can be built. By using an analysis matrix, we have case documentation available to us immediately. An analysis matrix can also provide us with pivot points for our timeline analysis; rather than combing through thousands of records in a timeline, we now not only have a means of going after that information which may be most important to our examination, but it also helps us avoid those annoying rabbit holes that we find ourselves going down sometimes.
Finally, consider this...trying to keep track of all of the possible artifacts on a Windows system can be a daunting task. However, it can be much easier if we were to compartmentalize various artifacts into categories, making it an easier task to manage by breaking it down into smaller, easier-to-manage pieces. Rather than getting swept up in the issues surrounding a new artifact (Jump Lists are new as of Windows 7, for example...) we can simply place that artifact in the appropriate category, and incorporate it directly into our analysis.
I've talked before in the blog about how to categorize various artifacts...in fact, in this post, I talked about the different ways that Windows shortcut files can be categorized. We can look at access to USB devices as storage access, and include sub-categories for various other artifacts.
Interested in Windows DFIR training? Check it out...Timeline Analysis, 4-5 Feb; Windows Forensic Analysis, 11-12 Mar.